Consider the national firestorm around Department of Agriculture official Shirley Sherrod last week. When a blogger posted a carefully edited video of a speech she made at an NAACP meeting, Sherrod's world fell apart. Bloggers and TV news media said that Sherrod, who is black, showed antipathy toward a white couple in the course of her job. After Sherrod was compelled to resign, the couple in question came forward to say she had actually helped them keep their farm. By the end of the week, Sherrod had a new job offer from the Agriculture Secretary and an apology from President Barack Obama.

Like most rumors, viral or not, Sherrod's smear began with a kernel of truth.

But according to snopes.com, a popular online destination for the facts behind rumors, reclaiming the truth isn't always a priority.

David Mikkelson, who runs snopes.com with his wife, Barbara, from their California home, recently told the New York Times: "It's not important whether things are true or not." Instead, he said, a rumor "reflects what people want to believe. It reflects a worldview. It's their way of passing along things that concern them. Things they're afraid of."

In other words, rumors say as much about the people who perpetuate them as they do about their subjects.

In Houston, perfume merchant Sajid Master got blindsided by a photo that went viral nearly a year ago, and he's still feeling the aftershock. The Muslim shopkeeper of Perfume Planet posted a sign on his door saying the store would be closed Sept. 11 to remember the death of sacred seventh-century Muslim leader Imam Ali. Someone took a photo of the sign, and it flew across the Internet.

Master still gets angry letters, phone calls and drop-ins from people who believe he's an al-Qaida sympathizer.

Some rumors are "tacit ways of expressing or reinforcing prejudices," said Mikkelson, in the same New York Times interview. "Maybe a crime rumor that has to do with gangs or Mexicans. And it's — 'Well, I'm not saying this about whatever group. It's the story I heard says that they're doing whatever.' It's sort of a camouflage."

Not all rumors, of course, are ad hominem attacks on individuals. Sometimes, the misinformation isn't harmful. It's just embellished or overblown.

When Denzel Washington visited Brooke Army Medical Center in San Antonio in 2004, for example, rumors swirled that the actor had written a massive check on the spot to fund a facility to house family members of service members undergoing medical treatment. Washington did write a generous check to the Fisher House Foundation, which operates a network of low-cost hotels on military medical center grounds - but he didn't bankroll a new building.

In his 2009 book, On Rumors: How Falsehoods Spread, Why We Believe Them, What Can be Done, legal scholar Cass Sunstein says electronic news sources offer "an architecture of control by which each of us can select a free-speech package that suits our interests."

Certainly, we can all relate. If you ask a roomful of people whether astronauts really walked on the moon or the Holocaust ever happened, you might get more than one answer. And if you do, that same group will disagree on other information as well.

For Sherrod, an ugly rumor had a quick turnaround and a positive ending: Her reputation was restored.